The Mariners placed Speier on the 15-day injured list Monday with left shoulder inflammation, Ryan Divish of The Seattle Times reports.
It's unclear how long Speier has been bothered by the shoulder issue, but he hasn't pitched since last Wednesday and was not sharp in that outing, retiring just two of six batters. Speier has been a workhorse out of the Seattle bullpen, so it's a sizable loss. He's made 15 appearances this season, posting a 2.92 ERA and 12:5 K:BB over 12.1 frames.